Semiconductor device with needle-shaped field plate structures

ABSTRACT

A semiconductor device includes a semiconductor substrate, a transistor cell region formed in the semiconductor substrate and an inner termination region formed in the semiconductor substrate and devoid of transistor cells. The transistor cell region includes a plurality of transistor cells and a gate structure that forms a grid separating transistor sections of the transistor cells from each other, each of the transistor sections including a needle-shaped first field plate structure extending from a first surface into the semiconductor substrate. The inner termination region surrounds the transistor cell region and includes needle-shaped second field plate structures extending from the first surface into the semiconductor substrate. The first field plate structures form a first portion of a regular pattern and the second field plate structures form a second portion of the same regular pattern.

BACKGROUND

In power semiconductor devices, for example IGFETs (insulated gate fieldeffect transistors) a load current typically flows in a verticaldirection between two load electrodes formed at opposite sides of asemiconductor die. In a blocking mode field plate structures extendingfrom one side into the semiconductor die deplete a drift portion of thesemiconductor die and facilitate higher dopant concentrations in thedrift portion without adverse impact on the blocking capability.Shrinking the field plate structures to needle-shaped field platestructures facilitates a grid-like gate structure between the fieldplate structures, wherein the grid-like gate structure provides a largertotal channel width per unit area than comparable stripe-shaped gatestructures.

It is desirable to improve reliable semiconductor devices withneedle-shaped field electrodes and low parasitic capacitances.

SUMMARY

According to an embodiment, a transistor cell region of semiconductordevice includes needle-shaped first field plate structures that extendfrom a first surface into a semiconductor portion that includes a driftstructure of a first conductivity type. An inner termination region,which surrounds the transistor cell region, includes needle-shapedsecond field plate structures. The inner termination region is devoid ofcounter-doped regions that are spaced from a second surface opposite tothe first surface. An outer termination region is sandwiched between anouter lateral surface of the semiconductor portion and outermostneedle-shaped second field plate structures.

According to another embodiment, an electronic assembly includes asemiconductor device, wherein a transistor cell region of thesemiconductor device includes needle-shaped first field plate structuresthat extend from a first surface into a semiconductor portion. Thesemiconductor portion includes a drift structure of a first conductivitytype. An inner termination region, which surrounds the transistor cellregion, includes needle-shaped second field plate structures. The innertermination region is devoid of counter-doped regions that are spacedfrom a second surface opposite to the first surface. An outertermination region is sandwiched between an outer lateral surface of thesemiconductor portion and outermost needle-shaped second field platestructures.

According to yet another embodiment, a semiconductor device comprises asemiconductor substrate, a transistor cell region formed in thesemiconductor substrate and an inner termination region formed in thesemiconductor substrate and devoid of transistor cells. The transistorcell region comprises a plurality of transistor cells and a gatestructure that forms a grid separating transistor sections of thetransistor cells from each other, each of the transistor sectionsincluding a needle-shaped first field plate structure extending from afirst surface into the semiconductor substrate. The inner terminationregion surrounds the transistor cell region and comprises needle-shapedsecond field plate structures extending from the first surface into thesemiconductor substrate. The first field plate structures form a firstportion of a regular pattern and the second field plate structures forma second portion of the same regular pattern.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description and onviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification. The drawings illustrate the embodiments ofthe present invention and together with the description serve to explainprinciples of the invention. Other embodiments of the invention andintended advantages will be readily appreciated as they become betterunderstood by reference to the following detailed description.

FIG. 1A is a schematic horizontal cross-sectional view of a portion of asemiconductor device including needle-shaped first field platestructures in a transistor cell region with source regions andneedle-shaped second field plate structures in a termination regionwithout source regions according to an embodiment.

FIG. 1B is a schematic vertical cross-sectional view of thesemiconductor device portion of FIG. 1A along line B-B.

FIG. 1C is an enlarged view of a detail of FIG. 1B.

FIG. 2A is a schematic perspective view showing the electrostaticpotential distribution in a portion of a semiconductor device with fiverows of needle-shaped second field plate structures in a terminationregion for illustrating effects of the embodiments.

FIG. 2B is a schematic perspective view showing the distribution ofimpact ionization in a portion of a semiconductor device with five rowsof needle-shaped second field plate structures in a termination regionfor illustrating effects of the embodiments.

FIG. 3A is a schematic perspective view showing the electrostaticpotential distribution in a portion of a semiconductor device with tenrows of needle-shaped second field plate structures in a terminationregion for illustrating effects of the embodiments.

FIG. 3B is a schematic perspective view showing the distribution ofimpact ionization in a portion of a semiconductor device with ten rowsof needle-shaped second field plate structures in a termination regionfor illustrating effects of the embodiments.

FIG. 4A is a schematic horizontal cross-sectional view of a portion of asemiconductor device according to an embodiment with narrow transitionregion and field stop layer.

FIG. 4B is a schematic vertical cross-sectional view of thesemiconductor device portion of FIG. 4A along line B-B.

FIG. 4C is an enlarged view of a detail of FIG. 4B.

FIG. 5 is a schematic vertical cross-sectional view of an outertermination region according to an embodiment referring to a drain fieldplate.

FIG. 6 is a schematic vertical cross-sectional view of a portion of asemiconductor device according to an embodiment with a gate connectorformed between portions of an interlayer dielectric.

FIG. 7 is a schematic horizontal cross-sectional view of a portion of asemiconductor device according to an embodiment concerning transistorcells with hexagonal cross-sectional area.

FIG. 8A is a schematic horizontal cross-sectional view of a portion of asemiconductor device according to an embodiment including five rows ofneedle-shaped second field plate structures in a termination region.

FIG. 8B is a schematic vertical cross-sectional view of thesemiconductor device portion of FIG. 8A along line B-B.

FIG. 9A is a schematic horizontal cross-sectional view of a portion of asemiconductor device including needle-shaped field plate structuresaccording to an embodiment with narrow-spaced field plate structures inthe termination region.

FIG. 9B is a schematic horizontal cross-sectional view of a portion of asemiconductor device including needle-shaped field plate structuresaccording to an embodiment with wide field plate structures in thetermination region.

FIG. 10 is a schematic circuit diagram of an electronic assemblyaccording to an embodiment related to switched-mode power supplies andmotor drives.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and in which are shownby way of illustrations specific embodiments in which the invention maybe practiced. It is to be understood that other embodiments may beutilized and structural or logical changes may be made without departingfrom the scope of the present invention. For example, featuresillustrated or described for one embodiment can be used on or inconjunction with other embodiments to yield yet a further embodiment. Itis intended that the present invention includes such modifications andvariations. The examples are described using specific language, whichshould not be construed as limiting the scope of the appending claims.The drawings are not scaled and are for illustrative purposes only. Forclarity, the same elements have been designated by correspondingreferences in the different drawings if not stated otherwise.

The terms “having”, “containing”, “including”, “comprising” and the likeare open, and the terms indicate the presence of stated structures,elements or features but do not preclude additional elements orfeatures. The articles “a”, “an” and “the” are intended to include theplural as well as the singular, unless the context clearly indicatesotherwise.

The term “electrically connected” describes a permanent low-ohmicconnection between electrically connected elements, for example a directcontact between the concerned elements or a low-ohmic connection via ametal and/or highly doped semiconductor. The term “electrically coupled”includes that one or more intervening element(s) adapted for signaltransmission may be provided between the electrically coupled elements,for example elements that are controllable to temporarily provide alow-ohmic connection in a first state and a high-ohmic electricdecoupling in a second state.

The Figures illustrate relative doping concentrations by indicating “−”or “+” next to the doping type “n” or “p”. For example, “n⁻” means adoping concentration which is lower than the doping concentration of an“n”-doping region while an “n⁺”-doping region has a higher dopingconcentration than an “n”-doping region. Doping regions of the samerelative doping concentration do not necessarily have the same absolutedoping concentration. For example, two different “n”-doping regions mayhave the same or different absolute doping concentrations.

FIGS. 1A to 1C refer to a semiconductor device 500 including a pluralityof identical transistor cells TC. The semiconductor device 500 may be ormay include an IGFET, for example an MOSFET (metal oxide semiconductorFET) in the usual meaning including FETs with metal gates as well asFETs with semiconductor gates, e.g., from polycrystalline silicon.According to another embodiment, the semiconductor device 500 may be anIGBT (insulated gate bipolar transistor) or an MCD (MOS controlleddiode).

The semiconductor device 500 is based on a semiconductor portion 100from a single crystalline semiconductor material such as silicon (Si),silicon carbide (SiC), germanium (Ge), a silicon germanium crystal(SiGe), gallium nitride (GaN), gallium arsenide (GaAs) or any otherA_(III)B_(V) semiconductor.

The semiconductor portion 100 has a first surface 101 which may beapproximately planar or which may be defined by a plane spanned bycoplanar surface sections as well as a planar second surface 102parallel to the first surface 101. A distance between the first andsecond surfaces 101, 102 depends on a voltage blocking capability thesemiconductor device 500 is specified for and may be at least 20 μm.According to other embodiments, the distance may be in the range ofseveral hundred μm. A lateral outer surface 103, which is tilted to thefirst and second surfaces 101, 102, connects the first and secondsurfaces 101, 102.

In a plane perpendicular to the cross-sectional plane the semiconductorportion 100 may have a rectangular shape with an edge length of severalmillimeters. A normal to the first surface 101 defines a verticaldirection and directions orthogonal to the vertical direction arehorizontal directions.

The semiconductor portion 100 includes a drain structure 130 thatincludes a drift structure 131 of a first conductivity type and acontact portion 139 between the drift structure 131 and the secondsurface 102. At least in portions of the vertical extension of the driftstructure 131 a dopant concentration may gradually or in steps increaseor decrease with increasing distance to the first surface 101. Accordingto other embodiments, the dopant concentration in the drift structure131 may be approximately uniform. A mean dopant concentration in thedrift structure 131 may be between 1E13 cm⁻³ and 1E18 cm⁻³, for example,in a range from 5E15 cm⁻³ to 1E17 cm⁻³. For a silicon-basedsemiconductor portion 100 the mean dopant concentration in the driftstructure 131 may be between 1E15 cm⁻³ and 1E17 cm⁻³, for example, in arange from 5E15 cm⁻³ to 5E16 cm⁻³.

The contact portion 139 may be a heavily doped base substrate or aheavily doped layer. Along the second surface 102 a dopant concentrationin the contact portion 139 is sufficiently high to form an ohmic contactwith a metal directly adjoining the second surface 102. In case thesemiconductor portion 100 is based on silicon, in an n-conductivecontact portion 139 the dopant concentration along the second surface102 may be at least 1E18 cm⁻³, for example at least 5E19 cm⁻³. In ap-conductive contact portion 139, the dopant concentration may be atleast 1E16 cm⁻³, for example at least 5E17 cm⁻³. For IGFETs andsemiconductor diodes, the contact portion 139 has the same conductivityas the drift structure 131. For IGBTs the contact portion 139 may havethe complementary second conductivity type.

The drain structure 130 may include further doped regions, e.g., a fieldstop layer or a buffer zone between the drift structure 131 and thecontact portion 139 or barrier zones.

A transistor cell region 610 includes the transistor cells TC, wherein agate structure 150 that forms a regular grid separates transistorsections TS of the transistor cells TC from each other. The gatestructure 150 may form a complete grid which meshes completely surroundthe transistor sections TS or may include gaps where connection sectionsof the semiconductor portion 100 form bridges between neighboringtransistor sections TS. According to the illustrated embodiment, thegate structure 150 forms a regular and complete grid and the transistorsections TS are formed in the meshes of the gate structure 150.

The gate structure 150 extends from the first surface 101 into thesemiconductor portion 100 and may include stripe-shaped gate edgeportions 153 as well as gate node portions 154. Within the transistorcell region 610 each gate edge portion 153 extends along one common edgeof two neighboring transistor sections TS. The gate edge portions 153have uniform width and are straight without bends. The gate edgeportions 153 may be formed along all edges of transistor sections TS ofall functional transistor cells TC within the transistor cell region610.

The gate node portions 154 connect two, three or more of the gate edgeportions 153 with each other and are formed at some or all of the nodesof the gate structure 150, wherein the gate structure 150 may includetwo or more different types of node portions 154.

The gate node portions 154 may be formed such that a minimum inner angleof the transistor sections TS is at least 120°, for example at least135°.

A horizontal cross-sectional area of the gate node portions 154 mayinclude stripe-shaped partial areas with a width of the gate edgeportions 153 and one, two, three or four isosceles triangular partialareas fitting between two of the stripe-shaped partial areas,respectively.

The gate node portions 154 are arranged such that each of the gate edgeportions 153 is connected to the other gate edge portions 153 throughconnections within the transistor cell region 610, through connectionsoutside of the transistor cell region 610, or through both connectionswithin the transistor cell region 610 and connections outside of thetransistor cell region 610.

The gate structure 150 includes a conductive gate electrode 155 thatincludes or consists of a heavily doped polycrystalline silicon layerand/or a metal-containing layer. The gate electrode 155 is completelyinsulated against the semiconductor portion 100, wherein a gatedielectric 151 separates the gate electrode 155 at least from bodyregions 120. The gate dielectric 151 capacitively couples the gateelectrode 155 to channel portions of the body regions 120. The gatedielectric 151 may include or consist of a semiconductor oxide, forexample thermally grown or deposited silicon oxide, semiconductornitride, for example deposited or thermally grown silicon nitride, asemiconductor oxynitride, for example silicon oxynitride, or acombination thereof. The gate electrode 155 is electrically connected orcoupled to a gate terminal G of the semiconductor device 500.

A vertical extension of the gate structures 150 may be in a range from100 nm to 5000 nm, for example in a range from 300 nm to 1000 nm. Ahorizontal width of the gate edge portions 153 may be in a range from100 nm to 1000 nm, for example, from 250 nm to 750 nm.

The transistor sections TS of the transistor cells TC are in the meshesof the gate structure 150 and include semiconducting portions of thetransistor cells TC as well as first field plate structures 160 thatextend from the first surface 101 into the semiconductor portion 100.Portions of the first field plate structures 160 between the firstsurface 101 and buried end portions may have approximately verticalsidewalls or may slightly taper at an angle of, e.g., 89 degree withrespect to the first surface 101. The sidewalls may be straight orslightly bulgy.

The first field plate structures 160 may be equally spaced alongparallel lines, wherein a plurality of first field plate structures 160with the same horizontal cross-section area may be arranged along eachline, and wherein the lines may be equally spaced.

Each first field plate structure 160 includes a conductive first fieldelectrode 165 and a first field dielectric 161 surrounding the firstfield electrode 165, respectively. The first field electrode 165includes or consists of a heavily doped silicon layer and/or ametal-containing layer. The first field dielectric 161 separates thefirst field electrode 165 from the surrounding semiconductor material ofthe semiconductor portion 100 and may include or consist of a thermallygrown silicon oxide layer, a deposited silicon oxide layer, e.g. asilicon oxide based on TEOS (tetraethyl-orthosilicate), or both.

A vertical extension of the first field plate structure 160 is smallerthan a distance between the first surface 101 and the contact portion139 such that the drift structure 131 may include a continuous driftsection 131 a between the first field plate structures 160 and thecontact portion 139 as well as columnar drift sections 131 b betweenneighboring first field plate structures 160. A vertical extension ofthe first field plate structures 160 is greater than a verticalextension of the gate structure 150. The vertical extension of the firstfield plate structures 160 may be in a range from 1 μm to 50 μm, forexample in a range from 2 μm to 20 μm. First horizontal extensions ofthe first field plate structures 160 may be in a range from 0.1 μm to 20μm, for example in a range from 0.2 μm to 5 μm, respectively.

The cross-sectional areas of the first field electrodes 165 and thefirst field plate structures 160 may be rectangles, regular or distortedpolygons with or without rounded and/or beveled corners, ellipses orovals. According to an embodiment, two orthogonal horizontal extensionsare approximately equal and the cross-sectional areas of the first fieldelectrodes 165 and the first field plate structures 160 are circles orregular polygons with or without rounded or beveled corners, such asoctagons, hexagons or squares.

The first field plate structures 160 allow high dopant concentrations inthe drift structure 131 without loss of blocking capability of thesemiconductor device 500. The needle-shaped first field electrodes 165increase the available cross-sectional area for the drift structure 131and reduce the on-state resistance RDSon compared to stripe-shaped fieldelectrodes.

The transistor sections TS with the semiconducting portions of thetransistor cells TC are formed in mesa sections of the semiconductorportion 100, protruding from a continuous section of the semiconductorportion 100 between the first field plate structures 160 and the secondsurface 102. A horizontal mean width of the mesa sections may be in arange from 0.2 μm to 10 μm, for example in a range from 0.3 μm to 1 μm.

Each transistor section TS includes a body region 120 of the secondconductivity type. The body regions 120 form first pn junctions pn1 withthe drain structure 130, e.g., the columnar drift sections 131 b, andsecond pn junctions pn2 with source regions 110 formed between the bodyregions 120 and the first surface 101. The body regions 120 completelysurround the first field plate structures 160 in a horizontal plane.Each body region 120 may include a heavily doped portion for forming anohmic contact with a metal contact structure.

The source regions 110 may be wells extending from the first surface 101into the semiconductor portion 100, for example into the body regions120. One source region 110 may surround the first field plate structure160 or two or more separated source regions 110 may be formed around thefirst field plate structure 160 in a horizontal plane. The sourceregions 110 may directly adjoin the first field plate structures 160 ormay be spaced from the first field plate structures 160.

The source regions 110 as well as the body regions 120 are electricallyconnected to a first load electrode 310. The first load electrode 310may be electrically coupled or connected to a first load terminal L1,for example the source terminal in case the semiconductor device 500 isan IGFET, an emitter terminal in case the semiconductor device 500 is anIGBT or an anode terminal in case the semiconductor device 500 is asemiconductor diode.

A second load electrode 320, which directly adjoins the second surface102 and the contact portion 139, may form or may be electricallyconnected to a second load terminal L2, which may be the drain terminalin case the semiconductor device 500 is an IGFET, a collector terminalin case the semiconductor device 500 is an IGBT or a cathode terminal incase the semiconductor device 500 is a semiconductor diode.

The first field electrodes 165 may be electrically connected to thefirst load electrode 310, to another terminal of the semiconductordevice 500, to an output of an internal or external driver circuit, ormay float. The first field electrodes 165 may also be divided indifferent subelectrodes which may be insulated from each other and whichmay be coupled to identical or different potentials.

In the illustrated embodiments and for the following description, thebody regions 120 are p-type, whereas the source regions 110 and thedrift structure 131 are n-type. Similar considerations as outlined belowapply also to embodiments with n-type body regions 120, p-type sourceregions 110, and a p-type drift structure 131.

When a voltage applied to the gate electrode 155 exceeds a presetthreshold voltage, electrons accumulate and form inversion channels inthe channel portions of the body regions 120 directly adjoining the gatedielectric 151 in the body regions 120. The second pn junctions pn2 withthe inversion channels get transparent for electrons in a forward biasedstate of the semiconductor device 500 with a positive voltage appliedbetween the drain structure 130 and the source regions 110 and a loadcurrent flows between the first and second load terminals L1, L2 invertical direction through the semiconductor device 500.

A termination region 690 without functional transistor cells TCsurrounds the transistor cell region 610 and may directly adjoin alateral outer surface 103 of the semiconductor portion 100. Thetermination region 690 is devoid of contact structures electricallyconnecting portions of the drift structure 131 directly or through pnjunctions or through unipolar homojunctions with the first loadelectrode 310.

The termination region 690 includes an inner termination region 692 thatsurrounds the transistor cell region 610 and that includes needle-shapedsecond field plate structures 170 extending into the drift structure 131in the termination region 690. The inner termination region 692 isdevoid of counter-doped regions that contain dopants of the conductivitytype of the body regions 120 and that are spaced from the second surface102. The term “counter-doped region” includes regions of theconductivity type of the body regions 120, which form pn junctions withthe drift structure 131, as well as regions of the conductivity type ofthe drift structure 131, in which a net dopant concentration is lowerthan in adjoining portions of the drift structure 131 and which formunipolar homojunctions with the drift structure 131.

No pn junctions or unipolar homojunctions are formed between the secondfield plate structures 170 or directly adjoining to the second fieldplate structures 170. Between and around the second field platestructures 170 the drift structure 131 does not contain dopants of acomplementary conductivity type. The dopant concentration is uniform orgradually decreases or increases along only one direction or only alongtwo orthogonal directions.

The inner termination region 692 may be completely devoid of doped zonesequivalent to the source regions 110 in position and dopantconcentration and/or may devoid of contact structures electricallyconnecting doped zones equivalent to source regions 110 with the firstload electrode 310 or with a node with a potential closer to that of thefirst load electrode 310 than to the second load electrode 320.

The second field plate structures 170 may consist of at least one ofinsulating and intrinsic semiconducting materials. According to theillustrated embodiment, at least some of or all second field platestructures 170 include a second field electrode 175 and a second fielddielectric 171 surrounding the second field electrode 175, respectively.

The second field electrode 175 may float or may be electricallyconnected to an auxiliary electrode 390 which may be connected to anauxiliary terminal AX of the semiconductor device 500, to an internalcircuit node or to an output of an internal driver circuit. According toanother embodiment, the auxiliary electrode 390 and the first loadelectrode 310 form a common electrode such that both the first and thesecond field electrodes 165, 175 are connected to the first loadelectrode 310 and the first load terminal L1.

The second field electrode 175 includes or consists of a dopedpolycrystalline silicon layer and/or a metal-containing layer. Thesecond field dielectric 171 separates the second field electrode 175from the surrounding semiconductor material of the semiconductor portion100 and may include or consist of a thermally grown silicon oxide layer.According to an embodiment, the second field dielectric 171 may includeor consist of a deposited silicon oxide layer, e.g. a silicon oxidebased on TEOS.

The first and second field dielectrics 161, 171 may have the samethickness and the same configuration, e.g., the same layer structure.For example, if both the first and the second field dielectrics 161, 171consist of thermally grown semiconductor oxide, e.g. silicon oxide, thethickness of the first field dielectrics 161 may be equal to thethickness of the second field dielectric 171. If the first and secondfield dielectrics 161, 171 include a deposited oxide layer, thethickness of the deposited oxide layer may be the same in the first andsecond field dielectrics 161, 171.

The vertical extension of the second field plate structures 170 is equalto or may be greater than the vertical extension of the first fieldplate structures 160. A horizontal cross-sectional area of the secondfield plate structures 170 may be equal to or greater than a horizontalcross-sectional area of the first field plate structures 160. Accordingto an embodiment the first and second field plate structures 160, 170may have the same horizontal cross-sectional shape and cross-sectionalarea and may be formed contemporaneously in the same photolithographyprocess.

Center points CP of the second field plate structures 170 and the firstfield plate structures 160 may be equally spaced such that the secondfield plate structures 170 and the first field plate structures 160complement each other in a regular pattern, wherein center-to-centerdistances between neighboring second field plate structures 170, betweenneighboring first and second field plate structures 160, 170 and betweenneighboring first field plate structures 160 are equal. The arrangementof the center points of the second field plate structures 170 may becongruent to the arrangement of the center points of a portion of thefirst field plate structures 160. In other words, the first field platestructures 160 form a first portion of a regular pattern and the secondfield plate structures 170 may form a second portion of the same regularpattern.

The number of rows of second field plate structures 170 in thetermination region 690 between the transistor cell region 610 and thelateral outer surface 103 may be between 2 and 21, for example between 5and 15. The termination region 690 further includes an outer terminationregion 698 sandwiched between the lateral outer surface 103 and theoutermost second field plate structures 170 of the inner terminationregion 692. The outer termination region 698 may include an edgeconstruction 350 that includes a conductive structure electricallyseparated from the first load electrode 310. The conductive structuremay be electrically coupled to the second load electrode 320 such thatduring operation of the semiconductor device 500 an electric potentialof the conductive structure is equal to or at least close to that of thesecond load electrode 320.

The outer termination region 698 may include counter-doped regions thatare spaced from the second surface 102 and that form pn junctions withthe drift structure 131, wherein the conductivity type of counter-dopedregions is the conductivity type of the body regions 120. According toanother embodiment, the outer termination region 698 is free ofcounter-doped regions that are spaced from the second surface 102 andthat form pn junctions with the drift structure 131. According to afurther embodiment, the outer termination region 698 is completely freeof counter-doped regions.

The outer termination region 698 may include trench structures thatextend from the first surface 101 into the semiconductor portion 100,wherein the trench structures may include conductive structureselectrically separated from the second field electrodes 175. Accordingto another embodiment, the outer termination region 698 is free oftrench structures that extend from the first surface 101 into thesemiconductor portion 100.

A transition region 650 that includes one or more body regions 120separating the drift structure 131 from the first surface 101 mayseparate the transistor cell region 610 and the termination region 690.The transition region 650 may be devoid of contact structureselectrically connecting doped regions in the semiconductor portion 100with the first load electrode 310 and may include further first orfurther second field plate structures 160, 170. The transition region650 is also devoid of controllable transistor cells TC and may becompletely devoid of doped zones equivalent to the source regions 110with respect to position and dopant concentration.

In the transition region 650 the gate structure 150 may includeconnection portions 157 forming end portions of the gate structure 150,wherein a width of the connection portions 157 may be greater than awidth of the gate edge portions 153.

Intersections of the first pn junctions pn1 between the body regions 120of the transition region 650 and an edge section 131 c of the driftstructure 131 and the first surface 101 form portions of the boundarybetween the transition region 650 and the termination region 690.

Each intersection between first surface 101 and first pn junction pn1runs from one second field plate structure 170 to a neighboring secondfield plate structure 170, wherein both second field plate structures170 have the same distance to the transistor cell region 610. In otherwords, an outer edge of the body region 120 at any side of thetransistor cell region 610 in the finalized semiconductor device 500cuts a row of second field plate structures 170. The position of theintersections between first surface 101 and first pn junctions pn1results from the position of an edge of an implant mask used forimplanting the dopants defining the body region 120 and the thermalbudget applied after the implant.

According to an embodiment, direct virtual connection lines betweenneighboring intersections between first surface 101 and first pnjunction pn1 cross central portions of the second field plate structures170, wherein a minimum distance between the center points of the secondfield plate structures 170 and the virtual connection lines is at most40%, e.g., at most 25% of a largest width of the second field platestructures 170 in the plane of the first surface 101.

In the inner termination region 692 and the transition region 650 nofurther structures are formed that need an additional process. Thetermination construction of the semiconductor device 500 gets alongwithout additional processes and thus combines high blocking capabilityof the termination region 690 with low fluctuations of the avalanchebreakdown voltage, high avalanche ruggedness and low process costs.

Alternatively, a continuous, stripe-shaped end trench may form a framethat completely surrounds the transistor cell region. For achieving highblocking capability and avalanche ruggedness, the vertical extension ofthe frame trench has to be tuned to the vertical extension of the fieldplate structures in the transistor cell region 610 and an additionalprocess has to be added to decouple the trench depth of the frame trenchfrom the trench depth of the needle-shaped field plate trench. Accordingto another alternative an additional process forms thicker fielddielectrics in the termination region than in a transistor cell region.By contrast, the termination construction of the semiconductor device500 ensures high blocking capability and avalanche ruggedness withoutadditional processes.

Finally, compared to a termination region with counter-doped regionsthat may be electrically connected to the second field electrodes, thedevice characteristics of the termination region 690 of semiconductordevice 500 are less susceptible to process variations.

FIG. 2A shows the electrostatic potential distribution in a terminationregion 690 including four rows of second field plate structures 170between the transition region 650 and the outer termination portion 698.An outer edge of the body region 120 overlaps with the innermost secondfield plate structures 170 of the inner termination region 692.

FIG. 2B shows impact ionization density in the avalanche case, wherein ahigh impact ionization density points to the location of the avalanchebreakdown. When the outer edge of the body region 120 runs betweensecond field plate structures 170 having the same distance to thetransistor cell region 610, most of the impact ionization takes placealong the outer edge of the outermost second field plate structures 170and close to the first surface 101.

FIGS. 3A to 3B show the electrostatic potential distribution and theimpact ionization density in case of avalanche breakdown for terminationregion 690 with ten rows of second field plate structures 170 formingthe inner termination region 692, wherein again the outer edge of thebody region 120 runs between second field plate structures 170 havingthe same distance to the transistor cell region 610.

While the electric field distribution is similar to that of FIG. 2A, thebreakdown is localized close to the bottom of the last active transistorcell in the transistor cell region 610. In such case avalanche currentmainly distributes equally and uniformly across the complete transistorcell region 610, avalanche behavior is comparatively stable and thesemiconductor device 500 shows high avalanche ruggedness.

In the semiconductor device 500 of FIGS. 4A to 4C the drain structure130 includes a field stop layer 135 sandwiched between the driftstructure 131 and the contact portion 139. A mean dopant concentrationin the field stop layer 135 may be at least five times as high as a meandopant concentration in the drift structure 131 and at most one-fifth ofa maximum dopant concentration in the contact portion 139. The auxiliaryelectrode 390 is directly connected with the first load electrode 310such that both the first and the second field electrodes 165, 175 areelectrically connected to the first load electrode 310 and the firstload terminal L1.

The transition region 650 may be formed between outermost portions ofthe gate structure 150 and the innermost second field plate structure170 of the termination region 690 such that in this embodiment thetransition region 650 does not include first or second field platestructures 160, 170. The first pn junction pn1 between the body region120 and the edge section 131 c of the drift structure 131 along thefirst surface 101 runs between portions of the gate structure 150 andthe innermost second field plate structures 170.

The edge construction 350 in the outer termination region 698 mayinclude a trench structure 230 that may extend from the first surface101 into the semiconductor portion 100. The trench structure 230 mayeffective as chipping stopper suppressing the propagation of cracks fromthe outer lateral surface 103 into the transistor cell region 610 and/orsuppressing the diffusion of ions from the outer lateral surface 103into the transistor cell region 610.

A vertical extension of the trench structure 230 may be smaller than,equal to, or greater than a vertical extension of the first field platestructures 160. The trench structure 230 may include several separatedstripe-shaped single trenches that are arranged to form one, two or moreframe-like structures at a distance to the outer lateral surface 103 andaround the inner termination region 692.

The trench structure 230 may be completely filled with an insulatormaterial, e.g., a silicon oxide or a spin-on-glass. According to anembodiment, an insulator layer may line sidewalls of the trenchstructure 230 and may insulate a conductive fill of the trench structure230 from the semiconductor portion 100. The conductive fill of thetrench structure 230 may float or may be electrically connected to astructure with an electric potential equal to or at least close to anelectric potential of the drift structure 131, for example the drainpotential in case the semiconductor device 500 is an IGFET. According toa further embodiment, the trench structure 230 includes an insulatorlayer along sidewalls of the trench structure 230 and a void in thecenter of the trench structure.

In FIG. 5 the edge construction 350 includes a trench structure 230 witha conductive fill 232 and an insulator layer 231 separating theconductive fill 232 from the semiconductor portion 100.

First and second termination contacts 351, 352 extend through theinterlayer dielectric 210 and electrically connect a terminationelectrode 355 with the conductive fill 232 and with a heavily dopedregion 235 formed in the semiconductor portion 100 along the firstsurface 101 in the outer termination region 698 such that the conductivefill 232 is electrically connected to the potential of the driftstructure 131. The heavily doped region 235 may also be effective aschannel stopper preventing the formation of parasitic channels along thefirst surface 101.

The outer termination region 698 may be completely free of counter-dopedregions between the lateral outer surface 103 and the outermost secondfield plate structures 170 of the inner termination region 692 as wellas between the field stop layer 135 and the first surface 101.

According to the illustrated embodiment, the outer termination region698 includes a counter-doped region 239 in an outer section 698 bdirectly adjoining the lateral outer surface 103 and separated from theinner termination region 692 by an inner section 698 a of the outertermination region 698, wherein the inner section 698 a is devoid ofcounter-doped regions. A width w3 of the inner section 698 a may be atleast 50% of a vertical extension v1 of the outermost second field platestructures 170, e.g., at least 100% of the vertical extension v1 suchthat no counter-doped region exists in the area of a depletion zone 199extending from the first pn junction into the drift structure 131.

In the outer termination region 698 a gate conductor 330 electricallyconnected to the gate electrodes of the transistor cells in thetransistor cell region may be between the auxiliary electrode 390 andthe lateral outer surface 103, or, if applicable, between the auxiliaryelectrode 390 and a termination electrode 355.

In the inner termination region 692, the interlayer dielectric 210 mayseparate an auxiliary electrode 390, which may be connected with a firstload electrode, from the semiconductor portion 100 and second contactstructures 316 extending through openings in the interlayer dielectric210 connect the auxiliary electrode 390 with the second field electrodes175.

In FIG. 6 the interlayer dielectric 210 separates the first loadelectrode 310 from the semiconductor portion 100. First contactstructures 315 may electrically connect the first load electrode 310with the source regions 110 and the body region 120 as well as with thefirst field electrodes 165 of the transistor cells TC in the transistorcell region 610. In a plane parallel to the first surface 101, across-section of the first contact structures 315 may includestripe-shaped sub portions, for example a frame of equal width and afurther stripe portion extending through the frame as indicated for onetransistor cell TC of FIG. 4A.

Second contact structures 316 may extend through the interlayerdielectric 210 and may directly electrically connect the auxiliaryelectrode 390 with the second field electrodes 175 in the terminationregion 690 and, if applicable, in the transition region 650.

The interlayer dielectric 210 may embed a gate conductor 330, wherein ina plane parallel to the cross-sectional plane gate contacts may extendfrom the gate conductor 330 to connection portions of the gate structure150. The gate conductor 330 may include a metal layer and/or a heavilydoped polycrystalline silicon layer.

According to another embodiment, the gate conductor 330 may be a metalstructure formed in the plane of the first load electrode 310 andlaterally separated from the first load electrode 310 and the auxiliaryelectrode 390 on top of the interlayer dielectric 210, wherein the gatecontacts extend through the complete interlayer dielectric 210.

The interlayer dielectric 210 adjoins the first surface 101 andelectrically insulates the gate electrode 155 from the first loadelectrode 310 arranged at the front side. In addition, the interlayerdielectric 210 may insulate mesa sections of the semiconductor portion100 in the termination region 690 from the auxiliary electrode 390.

The interlayer dielectric 210 may include one or more dielectric layersfrom silicon oxide, silicon nitride, silicon oxynitride, doped orundoped silicate glass, for example BSG (boron silicate glass), PSG(phosphorus silicate glass) or BPSG (boron phosphorus silicate glass),by way of example.

The first load electrode 310 may form or may be electrically coupled orconnected to the first load terminal, for example the source terminal incase the semiconductor device 500 is an IGFET. A second load electrode320, which directly adjoins the second surface 102 and the contactportion 139, may form or may be electrically connected to a second loadterminal, which may be the drain terminal in case the semiconductordevice 500 is an IGFET.

Each of the first load electrode 310, second load electrode 320,auxiliary electrode 390, and gate conductor 330 may consist of orcontain, as main constituent(s), aluminum (Al), copper (Cu), or alloysof aluminum or copper, for example AlSi, AlCu or AlSiCu. According toother embodiments, at least one of the first load electrode 310, secondload electrode 320, auxiliary electrode 390, and gate conductor 330 maycontain, as main constituent(s), nickel (Ni), tin (Sn), titanium (Ti),tungsten (W), tantalum (Ta), vanadium (V), silver (Ag), gold (Au),platinum (Pt), and/or palladium (Pd). For example, at least one of thefirst load electrode 310, second load electrode 320, auxiliary electrode390, and gate conductor 330 may include two or more sub-layers, whereineach sub-layer contains one or more of Ni, Sn, Ti, V, Ag, Au, Pt, W, andPd as main constituent(s), e.g., a silicide, a nitride and/or an alloy.

The first contact structures 315 as well as the second contactstructures 316 may include one or more conductive metal containinglayers based on, e.g., titanium (Ti) or tantalum (Ta) and a metal fillportion, e.g., based on tungsten (W). According to other embodiments thefirst and second contact structures 315, 316 include heavily dopedsemiconductor structures, e.g., heavily n-doped polycrystallinestructures or heavily p-doped columnar single crystalline structures.

FIG. 7 refers to an embodiment with hexagonal transistor cells TC. Thefirst and second field plate structures 160, 170 are arranged in shiftedlines with the center points of first and second field plate structures160, 170 in neighboring lines shifted against each other by the halfcenter-to-center distance d3, d4 within the lines.

In FIGS. 8A to 8B the inner termination region 692 includes six rows ofsecond field plate structures 170. The distance between neighboring rowsof second field plate structures 170 may be constant or may vary.

In FIG. 9A the transition region 650 includes one row of second fieldplate structures 170 and the termination region 690 includes 12 rows ofsecond field plate structures 170 per side of the transistor cell region610. Some of the outermost rows of second field plate structures 170have a center-to-center distance d2 which is smaller than the distanced1 between center points of neighboring rows of second field platestructures 170 close to the transistor cell region 610 by, e.g., atleast 10% of the distance d1. In addition, a vertical dopantconcentration in the drift structure 131 may decrease or increase withincreasing distance to the first surface 101 at least in the edgesection 131 c of the drift structure 131.

In FIG. 9B the first and second field plate structures 160, 170 have thesame distance d1 between center points. A mean horizontalcross-sectional area A2 of at least some of the second field platestructures 170 in a plane coplanar with the first surface 101 may begreater than a mean horizontal cross-sectional area A1 of the firstfield plate structures 160 by, e.g., at least 10% of A1. In addition, amean dopant concentration in the drift structure 131 may decrease orincrease with increasing distance to the first surface 101 at least inthe edge section 131 c.

FIG. 10 refers to an electronic assembly 510 that may be a motor drive,a switched mode power supply, a primary stage of a switched mode powersupply, a synchronous rectifier, a primary stage of a DC-to-ACconverter, a secondary stage of a DC-to-AC converter, a primary stage ofa DC-to-DC converter, or a portion of a solar power converter, by way ofexample.

The electronic assembly 510 may include two identical semiconductordevices 500 as described above. The semiconductor devices 500 may beIGFETs and the load paths of the two semiconductor devices 500 areelectrically arranged in series between a first supply terminal A and asecond supply terminal B. The supply terminals A, B may supply a DC(direct-current) voltage or an AC (alternating-current) voltage. Thenetwork node NN between the two semiconductor devices 500 may beelectrically connected to an inductive load, which may be a winding of atransformer or a motor winding, or to a reference potential of anelectronic circuit, by way of example. The electronic assembly mayfurther include a control circuit 504 configured to supply a controlsignal for alternately switching on and off the semiconductor devices500 and a gate driver 502 controlled by the control circuit 504 andelectrically connected to gate terminals of the semiconductor devices500.

The electronic assembly 510 may be a motor drive with the semiconductordevices 500 electrically arranged in a half-bridge configuration,wherein the network node NN is electrically connected to a motor windingand the supply terminals A, B supplying a DC voltage.

According to another embodiment, the electronic assembly 510 may be aprimary side stage of a switched mode power supply with the supplyterminals A, B supplying an AC voltage of an input frequency to theelectronic circuit 510. The network node NN is electrically connected toa primary winding of a transformer.

The electronic assembly 510 may be a synchronous rectifier of a switchedmode power supply with the supply terminals A, B connected to asecondary winding of the transformer and the network node NNelectrically connected to a reference potential of the electroniccircuit at the secondary side of the switched mode power supply.

According to a further embodiment, the electronic assembly 510 may be aprimary side stage of a DC-to-DC converter, e.g., a power optimizer or amicro-inverter for applications including photovoltaic cells with thesupply terminals A, B supplying a DC voltage to the electronic assembly510 and the network node NN electrically connected to an inductivestorage element.

According to another embodiment, the electronic assembly 510 may be asecondary side stage of a DC-to-DC converter, e.g., a power optimizer ora micro-inverter for applications including photovoltaic cells, whereinthe electronic circuit 510 supplies an output voltage to the supplyterminals A, B and wherein the network node NN is electrically connectedto the inductive storage element.

According to another embodiment a semiconductor device may include atransistor cell region with needle-shaped first field plate structuresthat extend from a first surface into a semiconductor portion thatincludes a drift structure of a first conductivity type. An innertermination region surrounds the transistor cell region and includesneedle-shaped second field plate structures. An outer termination regiondevoid of second field plate structures is sandwiched between a lateralouter surface of the semiconductor portion and outermost second fieldplate structures. In a transition region sandwiched between thetransistor cell region and the inner termination region a body region,which forms a first pn junction with the drift structure, directlyadjoins to the first surface. Intersections between the first pnjunction and the first surface run from one second field plate structureto a neighboring second field plate structure, wherein the two secondfield plate structures have a same distance to the transistor cellregion.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor substrate; a transistor cell region formed in thesemiconductor substrate and comprising a plurality of transistor cellsand a gate structure that forms a grid separating transistor sections ofthe transistor cells from each other, each of the transistor sectionsincluding a needle-shaped first field plate structure extending from afirst surface into the semiconductor substrate; and an inner terminationregion formed in the semiconductor substrate and devoid of transistorcells, the inner termination region surrounding the transistor cellregion and comprising needle-shaped second field plate structuresextending from the first surface into the semiconductor substrate,wherein the first field plate structures and the second field platestructures have the same layout.
 2. The semiconductor device of claim 1,wherein the gate structure forms a grid having meshes with gaps whichsurround the transistor sections, and wherein connection sections of thesemiconductor substrate form bridges between neighboring ones of thetransistor sections.
 3. The semiconductor device of claim 1, whereincenter-to-center distances between neighboring second field platestructures, between neighboring first and second field plate structures,and between neighboring first field plate structures are equal.
 4. Thesemiconductor device of claim 1, wherein the gate structure forms a gridhaving uninterrupted meshes which surround the transistor sections.
 5. Asemiconductor device, comprising: a semiconductor substrate; atransistor cell region formed in the semiconductor substrate andcomprising a plurality of transistor cells and a gate structure thatforms a grid separating transistor sections of the transistor cells fromeach other, each of the transistor sections including a needle-shapedfirst field plate structure extending from a first surface into thesemiconductor substrate; and an inner termination region formed in thesemiconductor substrate and devoid of transistor cells, the innertermination region surrounding the transistor cell region and comprisingneedle-shaped second field plate structures extending from the firstsurface into the semiconductor substrate, wherein the first field platestructures form a first portion of a regular pattern and the secondfield plate structures form a second portion of the same regularpattern.
 6. The semiconductor device of claim 5, wherein center pointsof the second field plate structures and center points of the firstfield plate structures are equally spaced such that the second fieldplate structures and the first field plate structures complement eachother in a regular pattern.
 7. The semiconductor device of claim 5,wherein the gate structure forms a grid having meshes with gaps whichsurround the transistor sections, and wherein connection sections of thesemiconductor substrate form bridges between neighboring ones of thetransistor sections.
 8. The semiconductor device of claim 5, whereincenter-to-center distances between neighboring second field platestructures, between neighboring first and second field plate structures,and between neighboring first field plate structures are equal.
 9. Thesemiconductor device of claim 5, wherein an arrangement of center pointsof the second field plate structures is congruent to an arrangement ofcenter points of a portion of the first field plate structures.
 10. Thesemiconductor device of claim 5, wherein the gate structure forms a gridhaving uninterrupted meshes which surround the transistor sections. 11.The semiconductor device of claim 5, further comprising: an auxiliaryelectrode and second contact structures electrically connecting, in thetermination region, the auxiliary electrode with second field electrodesin the second field plate structures.
 12. The semiconductor device ofclaim 11, wherein the auxiliary electrode is electrically connected witha first load electrode that is electrically connected with first fieldelectrodes in the first field plate structures.
 13. The semiconductordevice of claim 5, further comprising: a transition region interposedbetween the transistor cell region and the inner termination region, thetransition region forming a first pn junction with a drift structure ofthe transistor cell region, the first pn junction extending to the firstsurface of the semiconductor substrate.
 14. The semiconductor device ofclaim 13, wherein the first pn junction extends horizontally betweenneighboring ones of the second field plate structures aligned in a samerow, and wherein the second field plate structures in the same row havethe same distance to the transistor cell region.
 15. The semiconductordevice of claim 13, wherein the transition region comprises connectionportions of the gate structure.
 16. The semiconductor device of claim 5,further comprising: an outer termination region interposed between alateral outer surface of the semiconductor substrate and an outermostone of the second field plate structures, the lateral outer surfaceextending from the first surface to a second surface of thesemiconductor substrate.
 17. The semiconductor device of claim 16,wherein an outer section of the outer termination region is devoid ofregions of a second conductivity type that are spaced from the secondsurface of the semiconductor substrate and that form pn junctions with adrift structure of the transistor cell region.
 18. The semiconductordevice of claim 16, wherein the outer termination region comprises aconductive structure electrically connected to the drift structure. 19.The semiconductor device of claim 18, wherein the conductive structurecomprises a conductive fill of a trench structure extending from thefirst surface into the semiconductor substrate.
 20. The semiconductordevice of claim 18, wherein the conductive structure comprises a heavilydoped region directly adjoining the first surface.